title: Artesunate enhances the antibacterial effect of {beta}-lactam antibiotics against Escherichia coli by increasing antibiotic accumulation via inhibition of the multidrug efflux pump system AcrAB-TolC.
abstract: OBJECTIVE
  Occasionally, we found that artesunate enhanced the antibacterial effects of antibiotics in vitro. Therefore, the enhancement of various β-lactam antibiotics by artesunate against Escherichia coli and the possible mechanism were investigated in the present study.
  
  
  METHODS
  Antibacterial effects were observed using the serial 2-fold dilution method and dynamic bacterial growth. Daunomycin accumulation within E. coli was observed using fluorospectrophotometry and laser confocal scanning microscopy. AcrAB-TolC, AmpC and TEM-1 mRNA expression was observed using a PCR method. Antisense oligonucleotides (as-ODNs) targeting AcrB were designed and used to block AcrB gene expression within E. coli ATCC 35218.
  
  
  RESULTS
  Although artesunate itself had no antibacterial ability, artesunate significantly increased the antibacterial effect of β-lactam antibiotics against E. coli ATCC 35218 and an E. coli clinical strain. Artesunate increased daunomycin accumulation within E. coli ATCC 35218 in a dose-dependent manner and reduced the mRNA expression of AcrAB-TolC, an important multidrug efflux system for Gram-negative bacteria. The bacterial number was significantly reduced by as-ODN targeting AcrB, but did not further decrease after additional artesunate treatment. In contrast, artesunate lost its enhancement of β-lactam antibiotics against E. coli AG100A, a strain lacking the gene encoding AcrAB, and artesunate did not increase daunomycin accumulation within E. coli AG100A. After the transformation of pET28a-AcrB into E. coli AG100A, artesunate regained enhancement of β-lactam antibiotics. Furthermore, artesunate did not inhibit the expression of AmpC and TEM-1 mRNA.
  
  
  CONCLUSIONS
  Artesunate enhances the antibacterial effect of various β-lactam antibiotics against E. coli, which might be associated with the suppression of a major multidrug resistance system, AcrAB-TolC.
authors.affiliation: Department of Pharmacology, College of Pharmacy, The Third Military Medical University, and Medical Research Center, Southwestern Hospital, Chongqing 400038, PR China.
authors.forename: Bin
authors.initials: B
authors.lastname: Li
authors.forename: Qi
authors.initials: Q
authors.lastname: Yao
authors.forename: Xi-Chun
authors.initials: XC
authors.lastname: Pan
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Guofu
authors.initials: G
authors.lastname: Ding
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.forename: Chong
authors.initials: C
authors.lastname: Wu
authors.forename: Dongzhi
authors.initials: D
authors.lastname: Ran
authors.forename: Jiang
authors.initials: J
authors.lastname: Zheng
authors.forename: Hong
authors.initials: H
authors.lastname: Zhou
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D037621:Artemisinins / Q000494:pharmacology*; D000077332:Artesunate; D001425:Bacterial Outer Membrane Proteins / Q000037:antagonists & inhibitors*; D001692:Biological Transport / Q000187:drug effects; D003630:Daunorubicin / Q000378:metabolism; D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects*; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors*; D020869:Gene Expression Profiling; D008074:Lipoproteins / Q000037:antagonists & inhibitors*; D026901:Membrane Transport Proteins / Q000378:metabolism; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000037:antagonists & inhibitors*; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D037621:Artemisinins; D000077332:Artesunate; D001425:Bacterial Outer Membrane Proteins; D003630:Daunorubicin; D029968:Escherichia coli Proteins; D008074:Lipoproteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D047090:beta-Lactams; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C073126:tolC protein, E coli